Hepatitis C virus (HCV) is a highly successful pathogen that causes chronic hepatitis and hepatocellular carcinoma. Current therapies for treating HCV patients are frequently ineffective, and HCV-specific antivirals and vaccines are not yet available. New opportunities for targeting this pathogen are likely to come from a thorough understanding of the viral life cycle. We have recently developed a system to efficiently grow HCV in cell culture, allowing the viral life cycle to be fully dissected at the molecular level. We will use this system to examine how infectious virus particles are assembled. One key observation is that infectious HCV particles have an unusually low buoyant density, which is likely due to interaction with serum lipoproteins. In this proposal, we examine the hypothesis that HCV particle infectivity requires interaction with serum lipoprotein components during an intracellular step in virus formation. To address this hypothesis, we will define the composition of HCV particles (Aim 1);identify early steps in HCV particle assembly by using live and fixed cells imaging methods (Aim 2);and delineate the intracellular process of HCV particle maturation by using biochemical and cell biological methods (Aim 3). These studies will provide new insights into the nature of HCV particle infectivity and virus-host interaction. PUBLIC HEALTH RELEVANCE: Hepatitis C virus (HCV) is a highly successful human pathogen that causes persistent infection, chronic hepatitis, and hepatocellular carcinoma. Our studies characterize the virus particle and its interactions with the host cell, which will provide new avenues to target HCV.